Security devices and corresponding methods of use of the above kind are already known in the prior art.
Patent application GB 2 324 065 A discloses a security device comprising, for example, an epoxy resin in which small beads are embedded with a random distribution. Such devices however have become easy to reproduce, given their features and dimensions.
As another example, patent publication WO 2005/104008 discloses a security device comprising a medium in which taggants are embedded according to a random pattern. In a preferred embodiment, where the medium and the taggants react differently to an exposure to electromagnetic radiations, a representation of the random pattern may be obtained by exposing the device to such radiations. The obtained representation may then be compared to a previously recorded reference representation in order to authenticate the object carrying the security device.
The only practical example which is mentioned in this document relates to the mixing of a small amount of taggant particles with a liquid such as an ink.
The security device is based mainly on the fact that the taggants are invisible to the human eye, a specific detector being necessary to create the representation to be compared to the reference.
However, such an approach has now become usual and reproduction of the pattern is possible once the taggants have been identified and the appropriate detector found.
As another example, U.S. Pat. No. 5,907,144 describes a method to fabricate a micro bar-code on the edge of a magnetic disk for identification of defective items. The advantage of bar codes over alphanumerical characters is that the area required to write the ID number is much smaller. When marks are made for traceability purposes, the marks produced have to be as large as possible to enable an easy identification during fabrication (using optical microscopy). Since devices becomes smaller and smaller, the limiting factor concerning the maximal size achievable is the area available to make the mark. The bar codes take less space and less time to write than alphanumerical characters for the same amount of information. The techniques used to produce such bar codes generally involve laser scribe systems which permit the fabrication of features with sizes of tens of micrometers to few hundred of micrometers depending on the process. This approach would however not be appropriate in the case of anti counterfeiting since it would be easy to identify and reproduce the naming scheme or micropattern which is used.